Segmental abrasive wheel for pulp grinding



April 1 4, 1942.

L. A. PATT 'SEGMENTAL ABRASIVE WHEEL FOR PULP GRINDING 4 Sheets-Sheet 1Filed Dec. 14, 1939 jz a . INVENTOR. LEON A. PATT ATTORNEY.

April 14, 1942; v 1.. A.VPATT SEGMENTAL ABRASIVE WHEEL FOR PULP GRINDING4 Sheets-Sheet 2 Filed Dec. 14, 1959 LEON A. PATT BY ATTORNEY April 14,1942". PATT 2,279,486

SEGMENTAL ABRASIVE WHEEL FOR PULP GRINDING Filed Dec. 14, 1939 4Sheets-Sheet 3 It 4, A

, mvmon LEON A. PATT ATTORNEY.

April 14, 1942. PATT v 2,279,486

SEGMENTAL ABRASIVE WHEEL FOR PULP GRINDING Filed Dec. 14, 1939 4Sheets-Sheet 4 INVENTOR.

LEON A. PATT BY .ammmg ATTORNEY.

Patented Apr. 14, 1942 Q SEGMENTAL ABRASIVE WHEEL FOR PULP GRINDING LeonA. Patt, Sanborn, N. Y., assignor to The Carborundum Company, NiagaraFalls, N. Y., a corporation of Delaware Application December 14; 1939,Serial No. 309,217

7 Claims.

This invention relates to the manufacture of segmental abrasive wheelsand particularly to segmental abrasive wheels which, are used for themanufacture of wood pulp.

One of the objects of the present invention is Y to anchor the abrasivesegments as strongly as possible to a metal. hub whose mean radius ormean distance from the axis of rotation of the wheel is smaller than themean radius of the abrasive segments.

It has been a common expedient to clamp abrasive segments on a steeldrum or reinforced concrete center by means of clamping members whichpress on shoulders of the abrasive segments and which extend through thehub where nuts are used on the inside surface of the hub to apply thenecessary clamping pressure. Such methods of mounting the abrasivesegments usually involve extensive reduction of size of the segmentalbases with consequent danger of breakage of the segments under thestresses caused by the work of grinding, by changes of temperature, andby the pressure of the clamping means on shoulders disposed in the basesof the segments. If the supporting drum is close to the bases of theabrasive segments the mounting for the abrasive annulus is madecorrespondingly heavy. On this account reinforced concrete centers arefrequently provided for segmental wheels, and clamping means areextended from shoulders on the bases of the segments through theconcrete to steel hubs or supports of comparatively small radius. Oneobject of the present abrasive segments are illustrated by means of theaccompanying drawings in which:

I Figure 1 is a perspective view of an abrasive annulus assembly priorto the pouring of the concrete between the abrasive annulus and themetal hub;

Figure 2 is a perspective view of an abrasive segment with clampinghooks assembled in the segment; I

Figure 3 includes two fragmentary sections of an abrasive annulus takenin planes perpendicular to the axis of rotation, the smaller sectionbeing in a plane spaced from the clamping hooks;

Figure 4 is a section of the abrasive wheel on the line IV-IV of Figure3;

Figure 5 is a side view of an abrasive segment,

' showing a face whichis perpendicular to the axis invention is toprovide a set of .very strong anchors for each segment in wheels of thistype.

Another object is to provide connections be tween the segments and thehub or drivingsupport, which connections are substantially free' fromstress fluctuations due to temperature vari-- ations in the normaloperation of the wheel; These connections are obtained by using ametallic anchor hook or an anchor hook composed of a combination ofmetals to connect the abrasive segments to the driving hub. Thesemetallic connections are designed so that the accumulated thermalelongation of the metallic connection is J substantially equal to theaccumulated thermal elongation of the surrounding material that extendsbetween the seat of the hook in the segment and the driving hub of theabrasive wheel.

Improved means are also provided for transmitting torque from a concretecenter to the segments in the abrasive annulus.

The improvements in the mounting for the of rotation whenthe segment isplaced in position on the wheel mounting; v v

Figure 6 shows a radial face of an abrasive segment with two anchorhooks in position;

Figure '7 is a perspective view of an anchor I hook;

Figure 7a is a similar view of a modified form of anchor hook;

Figure 8 is a perspective view of a completed abrasive wheel containinga plurality of abrasive annuli;

Figure 9 shows a completed abrasive wheel mounted on a driving shaft;

Figure 10 is a fragmentary section taken in a plane perpendicular to theaxis and showing modified anchor hook connections between the concretecore andan abrasive segment;

Figure 11 is a fragmentary section on the line XB-XI of Figure-10 andFigure 12 is a view similar in part to Figure 10, showing a slightmodification of the latter.

Referringto the drawings in detail, abrasive segments 2 are assembled-ona horizontal surface .as shown in Figure 1 to form an abrasive annulus3. Each segment 2 is a bonded abrasive mass whose base is cut away toform grooves as indicated at 4 in Figure 2. Before the segments 2 arelaid in the position shown in Figure 1 their lower surfaces are sealedagainst water penetration from the concrete center by means of a coatingof a suitable sizing material, and they are provided with a number ofanchor hooks 5. These hooks may be made of a nickel-steel alloy whichhas approximately the same coefficient of thermalexpansion as theabrasive segments to which the hooks are attached. The hooks are bent(as shown at 6 in Figures 3 and 7) so that the short arm 'I of each hookis substantially parallel to the base of the abrasive segment in whichit is seated. The short arm of the hook is inserted-in a slightly largeropening 8 in its abrasive segment. One or more strips of resilientmaterial 9 are inserted in the openings 8 between the hooks 6 and thewall of the opening 8 in the abrasive segment as indicated in Figures 2,3 and 4. These resilient strips may be made of felt or of rubber-bondedfibrous material. ample of fibrous material which may be used. Theobject of these strips is to prevent the accumulation of destructivestresses between the anchor hook and the segment in which it issubsequently seated in the following manner.

into the openings 8 to'form seats for the short arms of the hooks 5. Thelocation of the hooks with respect to the segments and of the seats forthe short arms of the hooks is illustrated in Figure 3, where seats areindicated at 8.

In the abrasive annulus shown in Figure 1 the joints l between thesegments are composed of a resilient composition which can be' made byinserting one or more sheets of fibrous material that has beenimpregnated with rubber and vulcanized. These resilient sheets arecemented to the adjacent surfaces of the segments which are beingjoined. As shown in Figure 2, the ends of the hooks which extend fromthe abrasive segment toward the concrete center are threaded. Internallythreaded sleeves II are screwed onto the projecting ends of the hooksand are used to couple extension rods I2 to the hooks as shownparticularly in Figures 3 and 4. The extension rods l2 pass throughplates H which are disposed in contact with the inside surface of thehub rings ll. Nuts I5 on the threaded ends of the rods [2 are used tohold the plates i3 against the rings H. The sleeves it are covered withyieldable tubes 2|, and portions of the extension rods I 2 are coveredwith similar tubes 2| in the view shown in Figure 1 which illustratesthe mounting of an abrasive annulus prior'to the pouring of the concretewithin the ring of segments. Tubes 2|" surround the long arms of thehooks 5.

Sisal is an ex- O -Q melting metal, such as Babbitt metal, is poured Thegrooves 4 in the bases of adjacent abrasive segments are combined inpairs to permit the forupper left-hand corner of the drawings. Metalplates I! are indicated in Figures 1 and 3 as disposed in the-grooveslying between the bases of adjacent segments and as extended between thesleeves II. These plates I] serve to reinforce the portion of theconcrete which is poured into the grooves I and around the projectingstems of the hooks and their extensions. The concrete core is shown inFigure 3 as extending not only between the abrasive segments and thering l4 but also inside the ring and around the nuts l5 which are thusheld in locked position.

Before the concrete is poured, each of the nuts I5 is tightened by meansof a calibrated torque indicating wrench to give a definitepredetermined compression on the seat that separates the short arm 1 ofthe anchor hook 5 from the segment to which the anchor hook isconnected. Thus each ring of segments is tightly secured before theconcrete core is poured. This method of assembly therefore distinguishesit from certain methods known in the prior art where clamping rodsextending through a concrete core are tightened up, after the concretecore has been poured. In the case of a pulpjwheel manufactured by theapplicant's method, the setting of the concrete core takes place underfavorable conditions for obtaining a balanced condition of the segmentalwheel.

' Also, before thepouring of the concrete core, the bases of theabrasive segments are coated with a layer of waterproofing materialwhich prevents the water from leaching into the abrasive segments inthat region of the concrete core which is adjacent to the abrasivesegments. This arrangement has the general effect of preserving thesolidity and strength of the concrete adjacent the abrasive segments, aswell as preventing shrinkage of the concrete. This waterproofingmaterial impregnates a layer of each abrasive segment adjacent thecoated surface.

The concrete core is reinforced by means of metal rings or hoops 22 asshown in Figures 1 and 4. Suflicient metal reinforcement is used toadequately restrain the concrete core from appreciable or destructiveexpansion due to centrifugal stresses when in operation. In this way thesegments in the abrasive annuli are .not required to in any way restrainthe concrete core from bursting.

Towardthe left of Figure 3 a small section removed from but parallel tothe main section is shown. The small section shows particularly the'driving key 6 reinforced with the metal plate IT. The resilient layer I0is shown only on the trailing face of the key 16. The leading face ofthe key I6 is in contact with the adjacent segment 2. The arrow A inFigure 3 shows the direction in which the wheel is operated. Theconcrete projections l6 reinforced by the radially disposed plates I!have an important'function in transmitting torque from the concrete coreto the abrasive annulus which is made up of the abrasive segments 2.

In Figure 8 there is shown in perspective an abrasive wheel made up ofthree abrasive annuli. These annuli are separated by resilient annularjoints indicated by the reference character I8. Theseare similar to thejoints I0 described in some detail above. A plurality of abrasive annulican be assembled by providing them with a common ring or tube formed byjoining the. rings l4 in an axial direction. The abrasive annuli canalso be provided with a common core, in which case the concrete is notpoured until all the annuli have been assembled, along with the ringand-the anchor hook connections.

In the view shown in Figure 8 the segmental abrasive annuli are soassembled that the joints between the segments of the first annulus areoffset from those in the second annulus, while 4 the joints between thesegments in the third annulus are offset from the joints of the secondannulus and also from those of the first annulus. This same progressiveoffset relationship between segments in adjacent and successive abrasiveannuli can be maintained in assemblies that require a larger number forconvenience in construction.

It is also distinctlyadvantageous to have the planes between theintermediate annulus (or annuli) and the end annuli inclined at a slightangle to the end planes of the wheel as illustrated in Figure 9. Theinterannular planes are therefore not quite perpendicular to the axis ofthe wheel.

This arrangement tends to prevent the formation of grooves between thesegments and to reduce the localized wear on the wheel. In Figure 9there is also shown meansfor driving the completed abrasive wheel. Thedriving shaft 23 has a left-hand threaded engagement with the drivingflange 24 and a right-hand threaded engagement with the oppositelydisposed driving flange 25.

Increase of load on the wheel therefore tends to screw the drivingflanges more tightly against the wheel.

A resilient material is provided between all adjacent faces of theabrasive segments. These resilient joints afford a compensating factorfor gaged therewith to obtain a reliable assembly.

differential expansion ofthe concrete core with respect to the abrasivesegments. These resilient joints also afford a compensating factorforexpansion of the abrasive segments when they are subjected to theoperating temperatures produced Rings 14 confine all plates l3 asindicated in the drawing and hold them in definite position. The

working loads which are imposed on the segment anchorage will.betransmitted back to the rings M. This transmission of forces to therings will by heat generated byabrasion at the periphery of the stonewhen in use. The temperatures of the outer parts of the abrasivesegments may approximate those of boiling water. I

One of the principal advantages ofthe anchor hook attachments to asegment (illustratedpan ticularly in Figures 2 and 7) is found in thefact that only a small amount of material is removed from the segmentsto provide for the insertion of the hooks. The thickness of the abrasivebetween the seat of the hook (which may be made of Babbitt metal) andthe base of the abrasive segment may vary nearly half an inch withoutseriously weakening the abrasive segment. The radial thickness of one ofthe abrasive segments such as is shown in Figure 8 may be seven inchesor more. The applicant has made a number of tests of the tensilestrength of such an anchorage,

the outer portion of an abrasive segment being gripped and pulled in onedirection while the four hook-arms that extend from the base of thesegment are simultaneously pulled in the be readily appreciated oninspection of Figure 1, from which it can be seen that, when theassembled annulus is rotating, the various forces acting on the abrasivesegments are transmitted to and borne by the strong rings l4.Consequently th size and proportioning of these rings are vital andbasic factors which can be adjusted to meet' the"variations in speed orother operating are controlled principally by the size of the assembledgrinding wheel, as well as by the speed and other operating conditionsto which it may be subjected. In the design of thereinfaces as is shownclearly inF-igure 3. This 10- cation of the segment anchorage is quiteadvantageous as it places the anchoring means at the best geometricalpoints in the abrasive segment to effective'y resist centrifugal forcesand to secure each segment against the forces produced by the work loadof grinding. These forces tend to twist or'rotate the segments out oftheir assembled positions within the grinding wheel. These forces. areoften far in excess of the centrifugal forces acting on the segmentssince they are the resultants of the centrifugal forces and thereactions of the materials that are being ground and crushed. It isapparent, therefore, that the combination of a strong means of anchorageand the best mechanical application of that anchorage to individualsegments in the abrasive annuli is such'as to provide a distinctimprovement in the design and construction of segmental grinding wheels;forwhen so made they will withstand to an unusual degree the stressesincident to normal operation. It is evident, therefore, that theapplicants segmental anchorage is of such a character that it can resistvery great centrifugal forces when the abrasive wheel is in operation.

The segment anchorage means in this new and improved construction ofabrasive wheels consists of a plurality of units which are here shownand described as bimetallic members. Each bimetallic member consists ofa special nickel steel alloy anchor hcok 5 connected to an extension rodl2 by means of a threaded sleeve forcing structure of this pulp wheel,the actual amount of reinforcing of the concrete center will beprincipally that required to prevent the concrete center from anybursting caused by centrifugal stresses which occur in normal operationof the wheel. The concrete center could be rotated safely at operatingspeeds without the abrasiv segments. The wheel is designed'so that inthe completed. assembly normal operation of the wheel will not causerotational expan'sion of the center that would produce undue outwardpressure on the abrasive segments.

Another important feature of the wheel design is to be found in theoutside layer of steel coils or rings 31 which are located very close tothe outer surface of the concrete center for a purpose which will now beexplained The disposition of these rings or coils 31 is very importantsince they actually act as compression members which have been found toeffectively prevent appreciable shrinkage of the concrete while it iscuring or setting. This is believed to be a novel feature of the design.Others have built concret centered pulp stones, but have found itnecessary to tighten the abrasive segments onto the center after theconcrete had cured and shrunk. The compression of rings of the presentdesign eleminate any loosening up of the final assembly, as well as anytightening or adjusting such as has just been described in connectionwith prior practice.

The segmental abrasive annular assembly shown in Figure l is essentiallya self-sustaining member, as is also the concrete center. The concretecenter is indicated in Figures 3 and 4. When a grinding wheel soassembled is mounted as shown in Figures 8 and 9, the flanges 24 and 25grip the ends of the concrete center with sufllcient pressur to cause itto revolve. The

reinforced driving keys l6, being integral with N the concrete center,exert a driving torque on the abrasive segments 2, each of which is incontact with the. leading edge of a corresponding key l6 as shown in theupper left portion of Figure 3, wher the arrow A above the abrasivesegments indicates clockwise rotation.

Work load pressures in pulp grinding are applied (for example, by meansof a hydraulic piston) in a direction toward the axis of the wheel.Friction of the logs (being ground) against the grinding surface tendsto move the abrasive seg ments 2 in a direction opposite to the rotationof the wheel. The lugs I6, being in contact with portion of the long armof the anchor hook 5. It has been found thatwhen approximately onehalfof the combined length of the sleeve II and the rod l2 are encased inthe tubes 2| and 2|,

the segments, prevent such dislocation and transmit driving torque fromthe concrete center to the abrasive annulus or annuli. The principalfunction of the anchoring means is to hold the abrasive segments tightlyon the surface of the concrete center. The anchoring means is pro- 1sity for compensating in any way for differences in thermal expansionbetween the abrasive segments and the concrete center. The abrasivesegments have a lower coeflicient of thermal expansion than the concretecenter. Assuming uniform increase of temperature, the abrasive segmentswill expand radially at the same rate as the anchor hooks 5, and theconcrete center will expand radially at the sam rate as the extensionrods l2. This arrangement in which the anchor hooks 5 have the samecoefficlent of thermal expansion as the surrounding abrasive segmentsand in which the extension rods |2 have the same coefllcient of thermalexpansion as the surrounding concrete center therefore protects theabrasive segments and the anchoring means from radial stresses duringchange of temperature. During increase of temperature there will be atendency for the abrasive segments to separate in both axial andcircumferential directions. It is desirable, therefore, that thecombined member l2 and 5 should be able to bend slightly. To accomplishthis result, .the long arm of the anchor hook 5, the sleeve H and theradially outward portions of the rod |2 are mounted within yieldabletubes 2|", 2|, and 2| as shown in Figures 1, 3 and. 4 so as to actuallyseparate these metal parts from rigid surrounding materials. The tubes2|, 2|, and 2|" may be made of paper or other compressible material astheir function is to permit the rods |2 to remain in a straight line orto bend slightly so that undue stresses will not be built up in theabrasive segments or in the anchoring means during changes oftemperature.

The actual length of the tube-encased portion of the anchorage means isonly such as to avoid dangerous stress concentration in the anchoragemeans. Even though the encasing tubes will eliminate actual contactbetween the concrete and the sleeve N, there is another factor that mustbe recognized. The length of the encased portion of the anchoragev meansis related to the stress concentration at the ends of the threadedportions of the hooks 5 and rods 2. If nearly the entire length of therod |2 were free to move laterally, the flexural stresses within theanchorage means would be small.

On the other hand, if the rods I2 and the sleeves I were to be embeddeddirectly within the concrete for their entire length, then the fiexuralstresses in the anchorage means would reach such high values as to beunsafe, since there would be excessive stress concentration at thethreaded as shown in the drawings, the flexu'ral stresses within theanchorage means remain within the limits usually considered safe formechanical members of this class. Factors such a the size of theassembled wheel, fluctuations in the operating temperature, and thethermal expansion or other physical characteristics of the constructionmaterials must all be considered and evaluated when determining theactual lengths of the tubes 2| and 2|. For the purpose of elimination ofvibration, it is preferred to embed the inner portions of the rods l2substantially as shown in the drawings. In any case the long arm of thehook 5 is partially encased within a tube made of yieldable material.Due to the relatively short length of the hook in the member 5 it isessential that freedom for lateral movement be'provided for the hookwithin the recess in the abrasive and particularly where it passesthrough the driving key |6. Hence the tube 2|" surrounds this portion ofthe hook.

It will be noted that in the case of pulp wheel structures of the typedisclosed in this application, thermal stresses within an assembly maybuild up to destructive values in the absence of suitable means forreducing such stresses. The magnitude of such stresses is often fargreater than the purely mechanical stresses incident to normaloperation. Such stresses are likely to cause failure, especially nearthe junction of the abrasive segments and of the concrete center. Theuse of yieldable tubes to greatly reduce or to prevent the building upof such stresses to a dangerous point is therefore considered a vitalpart of the invention.

In the modification illustrated, in Figures 10 and 11 the anchor hooks5' are integral with the bolts I 2'. Each bolt I2 is surrounded by astrong metal sleeve 3|. The sleeve 3| extends between a shoulder 32 onthe anchor hook and a plate 33. By tightening the nut 34 the bolt |2'can be put under tension. I

While the segments (with the attached anchor hooks, bolts, plates andnuts) are being assembled into an abrasive annulus, preloading of radialjointsis accomplishedby external application of radial pressure by meansof clamping bands, etc. The bolts |2 are placed under tension by meansof the nuts 34. The concrete is poured within the abrasive annulus andaround the inwardly projecting sleeves 3| and the annular reinforcements35. The external pressure is removed after the concrete has set. Thehooks 5 project into openings 8 in the sides of the segments in the samemanner as shown in Figure 3. The hook is seated on the abrasive segmentby means of Babbitt metal or the like at 36. Resilient strips 9 are usedas described in connection with Figures 2 and 3.

In the modification shown in Figure 12 .the

sleeves 3| project beyond the concrete to the bends in the anchor hooks.

Other advantages of the applicant's improved segmental wheel will beapparent from the foregoing description taken in connection with thedrawings. The invention is defined within the a of the a substantiallylarger coemcient of thermal expansion than the abrasive segments, aplurality of anchor hooks each having a curved end that is seated in anopening in the side of an abrasive segment and having the opposite endadapted for supporting said abrasive segments, and a pluralityofbimetallic anchor hooks in each of which a short arm rests on a seatin a corresponding abrasive segment while the long arm forms an anglewith said short arm andis at-o tached to a strong support embedded inthe conwhile the traiiing iace of the key is connected to the rim bymeans 01', a resilient layer, and anchor hooks connecting the abrasivesegments with the wheel hub ring, each of said hooks having a bentportion seated in a lateral face of a segment and an inwardly extendedportion which is clamped. to the wheel hub ring and surrounded by theconcrete core.

'5. A segmental abrasive wheel comprising a plurality of segmentsforming an abrasive rim, a concrete core for said abrasive rim, anannular hub coaxial with said abrasive rim and separated therefrom bythe bulk of the concrete core, a plurality-'91 hookswhich grip eachsegment in positions distributed symmetrically about the segment byinsertion incylindrical openings in radial races of the segments, saidhooks being comcrete center, the stresses in the hook due to changes intemperature being rendered substantially tree from fluctuation by makingthe hook oftwo materials, one of which has approximately the samecoeflicient oi. thermal expansion as the surrounding abrasive segmentswhile the other part has substantially the same coeflicient or expansionas the surrounding concrete, and the I intermediate portion or theanchor book being separated irom its rigid surroundings by means oftubes of yieldable material.

3. A segmental wheel comprising a plurality of abrasive segments, aconcrete center for supporting said abrasive segments, and a pluralityof bimetallic anchor hooks for holding each segment to the concretesupport, each of said hooks havingashortarmseatedinanopeninginitsabrasive segment, the opening being only slightly larger than theenclosed portion of the hook and of small dimensions as compared withthe dimensions of the segment, and the portion of the hook which issurrounded by the segment having substantially the same coemcient ofexpansion as the segment while the remainder of the hook hassubstantially the same coeiiicient of expansion as the surroundingconcrete.

4. A segmental abrasive wheel having a rim comprised of a plurality ofabrasive segments connected by means or resilient joints, a hub ring forthe abrasive wheel sive rim, a concrete core connecting the abrasive rimwith the wheel hub rim, one or more reini'orced concrete keys projectingfrom the concrete core into the abrasive rim,

key being in direct contact with the rim disposed within the abratheleading lace posed of material having substantially the same coeflicientoi expansion as the abrasive segments and extending to the concretecore, connecting rods attached to the gripping hooks near the bases ofthe segments and extending through the concrete core and the annularhub, said connecting rods having about the same coeiiicient of expansionas the concrete, and means for placing 'said'connecting rods undertension to draw the gripping hooks tightly against seats in thecylindrical openings in the faces 01' the abrasive segments.

6. A segmental abrasive wheel having a rim comprised of a plurality ofabrasive segments connected by means of resilient joints, a hub ring foranchoring the abrasive rim, and a plurality of anchor hooks connecting,the abrasive segments with the hub ring, each of said anchor hookshaving a bent portion seated in an opening in a lateraliace or a segmentand an inward extension which is connected to the supporting hub ring,the portion oi the anchor hook which is seated in and adjacent to anyabrasive segment having approximately the same coefllcient of expansionas the abrasive segment.

7. A segmental. abrasive wheel having a rim comprised of a plurality ofabrasive segments connected by means of resilient joints, a hub ring forthe abrasive wheel disposed within the abrasive rim, a concrete coreconnecting the abrasive.

the concrete. v LEONAPA'I'I.

